1. Field of the Invention
The invention relates to a sampling circuit, and more particularly to a sampling circuit with offset cancellation and low-frequency noise cancellation.
2. Description of the Related Art
Generally, a sampling circuit with an operational amplifier (opamp) has a problem of opamp offset. In order to eliminate opamp offset in a sampling circuit, the operational amplifier is generally placed in a unit-gain feedback loop. However, the unit-gain feedback loop restricts the input common mode voltage and the output common mode voltage of the operational amplifier to be equal, which limits the type of operational amplifiers used in the sampling circuit. Moreover, because the gain of the sampling circuit is limited to be “1”, the gain cannot be adjusted according to system requirements.
Thus, it is desired to provide a sampling circuit with an operational amplifier, which has opamp offset cancellation functionality and adjustable gain and can operate under different input and output common mode voltages.